Studies of long-term survivors of cancer treated with radiation therapy and chemotherapy have led to important insights into carcinogenesis. In the past year, we have completed the analysis of a large study of survivors of small cell carcinoma of the lung. Similar to our previous smaller study, continued smoking appeared to be a risk factor for developing a second lung cancer. Overall, the risk of all cancers was threefold increased, sevenfold among smoking-related cancers, and no increase among nonsmoking related cancers. The cumulative risk of a second lung cancer reached 40% at 13 years after small cell cancer among the survivors. There was also evidence of synergism between continued smoking and chest irradiation in the development of lung cancer. Data collection was completed on two other cohort studies and is currently under analysis.